1. Field of the Invention
The present invention relates to a release lined pressure sensitive adhesive (PSA) flexible graphite product and, in particular, to a release lined PSA flexible graphite sheet article for thermal interface applications wherein the thermal properties of the flexible graphite sheet article are not significantly affected by a pressure sensitive adhesive used to bond the flexible graphite and which release liner is easily removed when the sheet is to be used without any significant delamination of the flexible graphite.
2. Description of Related Art
Flexible graphite is a well-known material used in a variety of industrial, commercial and domestic applications because of its chemical inertness and unique electrical and thermal conduction properties. It is of particular use as a gasketing or sealing material in automobile engines, piping flanges and vessel joints and as a fire proof covering for walls or floors, filtering devices for an air bag for generators, etc. wherein thin flexible graphite sheets between typically 2-70 mil are cut into various sizes to use from the product.
The process for manufacturing flexible graphite is well-known and the typical practice is described in U.S. Pat. No. 3,404,061 to Shane et al., the disclosure of which is incorporated herein by reference. In general, flakes of natural graphite are intercalated in an acid solution. After the flakes are intercalated they are washed and dried and then exfoliated by exposure to a high temperature or under a flame for a short period of time. This causes the flakes to expand or exfoliate in a direction perpendicular to the crystalline planes of the graphite. The exfoliated graphite flakes are vermiform in appearance and are therefore commonly referred to as worms. The worms may be compressed into sheets or foils with a density approaching theoretical density although a density of about 70 lbs/ft.sup.3 is considered typical for most applications. The sheets of flexible graphite can be cut into any desired configuration to suit a particular application.
New applications requiring a low thermal resistance interface sheet material include thermal joints and heat sinks A typical use is to thermally connect a computer chip to a cooling module. Flexible graphite is readily applicable to such applications because of its low thermal resistance and its ability to conform to the surfaces to be interfaced, especially when either or both surfaces are not completely flat. Prior art self bonding flexible graphite sheet articles typically use a PSA backing with a Mylar film as the adhesive carrier. This type sheeting however is not desirable for applications requiring low thermal resistance because the adhesive carrier cannot be cut and processed easily and the adhesive carrier has an extremely high thermal resistance. Additionally, twice the amount of adhesive is needed since there is adhesive on both sides of the Mylar carrier film. The sheeting also lacks mechanical integrity since the carrier film and adhesive typically readily separate from the flexible graphite substrate.
Bearing in mind the problems and deficiencies of the prior art it is therefore an object of the present invention to provide a release lined pressure sensitive adhesive flexible graphite article of manufacture and, in particular, a thermal interface sheet article having a low thermal resistance and which release liner is easily removed when the sheeting is to be used without any significant delamination of the flexible graphite substrate.
It is another object of the present invention to provide a method of making a release lined pressure sensitive adhesive flexible graphite article of manufacture, particularly a thermal interface sheet article having a low thermal resistance and which release liner is easily removed when the sheeting is to be used without any significant delamination of the flexible graphite substrate.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.